System, method, and computer program for creating united cellular lattice structure

ABSTRACT

A method for generating a computer-based united cellular lattice structure includes dividing a part volume into a number of adjacent subvolumes each having a side combination corresponding to a number and orientation of adjoining sides and non-adjoining sides. A modified lattice cell may be generated from a base lattice cell for each side combination of the subvolumes such that each modified lattice cell has face surfaces on faces thereof corresponding to non-adjoining sides and does not have face surfaces on faces thereof corresponding to adjoining sides. Copies of the modified lattice cells may then be generated and inserted into corresponding subvolumes such that the faces of the modified lattice cell copies having face surfaces are positioned along non-adjoining sides of the subvolumes and faces of the modified lattice cell copies not having face surfaces are positioned along adjoining sides of the subvolumes.

BACKGROUND

Complex parts formed via additive manufacturing and similar techniquesoften incorporate united cellular lattice structures for reducingoverall weight, increasing strength, and improving other properties ofthe parts. The united cellular lattice structures are modeled by mergingtogether a large number of lattice cells. Each individual lattice cellincludes a number of face surfaces that adjoin face surfaces of adjacentlattice cells. These adjoining face surfaces (i.e., “shared facesurfaces”) are not needed and thus are often removed when the latticecells are merged together. Creating and removing the shared facesurfaces is time intensive and significantly slows or delays computationof the united lattice cellular structures. It is also difficult todetermine if all of the adjoining face surfaces have been removedproperly, resulting in some adjoining face surfaces accidentally notbeing removed. This may result in computational or rendering errors oreven additive manufacturing errors. For example, additive manufacturingmaterial may be deposited incorrectly resulting in structuralweaknesses, inadequate seals, weight imbalances, and otherimperfections.

SUMMARY

Embodiments of the invention solve the above-mentioned problems andprovide a distinct advance in the art of additive manufacturing systemsand processes. More particularly, the invention provides a computermodeling and additive manufacturing system for creating a cellularlattice structure without searching for and removing shared or adjoiningface surfaces of lattice cells of the cellular lattice structure.

An embodiment of the invention is a method of generating acomputer-based united cellular lattice structure. The method includesdividing a part volume into a number of adjacent subvolumes. Eachsubvolume has a side combination corresponding to a number andorientation of adjoining sides and non-adjoining sides. A base latticecell having face surfaces corresponding to a face of the base latticecell may also be generated or received. A modified lattice cell may begenerated from the base lattice cell for each side combination of thesubvolumes such that each modified lattice cell has face surfaces onfaces thereof for non-adjoining sides and does not have face surfaces onfaces thereof for adjoining sides. Copies of the modified lattice cellsmay then be generated and inserted into corresponding subvolumes suchthat the faces of the modified lattice cell copies having face surfacesare positioned along non-adjoining sides of the subvolumes and the facesof the modified lattice cell copies not having face surfaces arepositioned along adjoining sides of the subvolumes. In this way, theunited cellular lattice structure may be created without computerprocessing intensive searching and removal of shared face surfaces. Thechances of imperfections and errors being introduced into renderings ofthe united cellular lattice structure and/or the united cellular latticestructure itself are also significantly reduced.

Another embodiment of the invention is a method of creating a partaccording to a computer-based united cellular lattice structure viaadditive manufacturing. The computer-based united cellular latticestructure may be formed by dividing a part volume into a number ofadjacent subvolumes each having a side combination corresponding to anumber and orientation of adjoining sides and non-adjoining sides. Abase lattice cell having face surfaces corresponding to a face of thebase lattice cell may also be generated or received. A modified latticecell may be generated from the base lattice cell for each sidecombination of the subvolumes such that each modified lattice cell hasface surfaces on faces thereof for non-adjoining sides and does not haveface surfaces on faces thereof for adjoining sides. Copies of themodified lattice cells may then be generated and inserted intocorresponding subvolumes such that the faces of the modified latticecell copies having face surfaces are positioned along non-adjoiningsides of the subvolumes and the faces of the modified lattice cellcopies not having face surfaces are positioned along adjoining sides ofthe subvolumes. The modified lattice cells may then be joined or mergedto form the united cellular lattice structure. The part may then beformed by depositing additive manufacturing material in successivelayers according to the united cellular lattice structure.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Other aspectsand advantages of the present invention will be apparent from thefollowing detailed description of the embodiments and the accompanyingdrawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments of the present invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a perspective view of a computer modeling and additivemanufacturing system constructed in accordance with an embodiment of thepresent invention;

FIG. 2 is a block diagram of selected components of the computermodeling system of FIG. 1;

FIG. 3 is a perspective view of the additive manufacturing system ofFIG. 1;

FIG. 4 is a perspective view of a part volume modeled via the computermodeling system of FIG. 1;

FIG. 5 is a perspective view of the part volume of FIG. 4 divided intosubvolumes;

FIG. 6 is a perspective view of a base lattice cell including facesurfaces;

FIG. 7 is a perspective view of a modified base lattice cell includingsome of the face surfaces removed;

FIG. 8 is a perspective view of copies of modified base lattice cellspositioned in the subvolumes of FIG. 5;

FIG. 9 is a perspective view of a united cellular lattice structureformed from the modified base lattice cell copies of FIG. 8;

FIG. 10 is a flow diagram of a method of creating a united cellularlattice structure in accordance with another embodiment of theinvention;

FIG. 11 is a flow diagram of a method of forming a united cellularlattice structure in accordance with another embodiment of theinvention;

FIG. 12 is a flow diagram of a method of forming a united cellularlattice structure in accordance with another embodiment of theinvention;

FIG. 13 is a perspective view of finite elements modeled via thecomputer modeling system of FIG. 1;

FIG. 14 is a chart of global and local node numbers for the finiteelements of FIG. 13; and

FIG. 15 is a chart of local node numbers, face numbers, and planesassociated with faces of the finite elements of FIG. 13.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following detailed description of the invention references theaccompanying drawings that illustrate specific embodiments in which theinvention can be practiced. The embodiments are intended to describeaspects of the invention in sufficient detail to enable those skilled inthe art to practice the invention. Other embodiments can be utilized andchanges can be made without departing from the scope of the presentinvention. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the present invention is definedonly by the appended claims, along with the full scope of equivalents towhich such claims are entitled.

In this description, references to “one embodiment”, “an embodiment”, or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment”, “an embodiment”, or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Forexample, a feature, structure, act, etc. described in one embodiment mayalso be included in other embodiments, but is not necessarily included.Thus, the current technology can include a variety of combinationsand/or integrations of the embodiments described herein.

Turning to the drawing figures, and particularly FIGS. 1-3, a computermodeling and additive manufacturing system 10 constructed in accordancewith an embodiment of the present invention is illustrated. The computermodeling and additive manufacturing system 10 broadly comprises acomputer aided design (CAD) system 12 and an additive manufacturingsystem 14.

The CAD system 12 may be used for designing and generating a computermodel of a part 100 and broadly includes a processor 16, a memory 18, atransceiver 20, a plurality of inputs 22, and a display 24. The CADsystem 12 may be integral with or separate from the additivemanufacturing system 14.

The processor 16 generates data representative of the computer model ofthe part 100 according to inputs and data received from a user. Theprocessor 16 may include a circuit board, memory, display, inputs,and/or other electronic components such as a transceiver or externalconnection for communicating with external computers and the like.

The processor 16 may implement aspects of the present invention with oneor more computer programs stored in or on computer-readable mediumresiding on or accessible by the processor. Each computer programpreferably comprises an ordered listing of executable instructions forimplementing logical functions and generating and manipulating datarepresentative of part models, part volumes, subvolumes, modelingframes, metadata, and other data in the processor 16. Each computerprogram can be embodied in any non-transitory computer-readable medium,such as the memory 18 (described below), for use by or in connectionwith an instruction execution system, apparatus, or device, such as acomputer-based system, processor-containing system, or other system thatcan fetch the instructions from the instruction execution system,apparatus, or device, and execute the instructions.

The memory 18 may be any computer-readable non-transitory medium thatcan store the program for use by or in connection with the instructionexecution system, apparatus, or device. The computer-readable medium canbe, for example, but not limited to, an electronic, magnetic, optical,electro-magnetic, infrared, or semi-conductor system, apparatus, ordevice. More specific, although not inclusive, examples of thecomputer-readable medium would include the following: an electricalconnection having one or more wires, a portable computer diskette, arandom access memory (RAM), a read-only memory (ROM), an erasable,programmable, read-only memory (EPROM or Flash memory), an opticalfiber, and a portable compact disk read-only memory (CDROM).

The transceiver 20 may transmit data and instructions between the CADsystem 12 and the additive manufacturing system 14. Alternatively, awired or integrated setup may be used between the CAD system 12 and theadditive manufacturing system 14.

The inputs 22 allow a user to design and modify a model of the part 100and may comprise a keyboard, mouse, trackball, touchscreen, buttons,dials, virtual inputs, and/or a virtual reality simulator. The inputs 22may also be used to control or instruct the additive manufacturingsystem 14.

The display 24 may display a two-dimensional or three-dimensionalrepresentation of the model and may also display model data, computeroptions, and other information via a graphical user interface (GUI). Thedisplay 24 may be separate from or integrated with the additivemanufacturing system 14.

The additive manufacturing system 14 produces prototypes and parts suchas part 100 and broadly comprises a frame 26, a support surface 28, amaterial reserve 30, a feeder 32, a material applicator 34, a set ofmotors 36, and a processor 38. The additive manufacturing system 14 maybe integral with or separate from the computer aided design system 12.

The frame 26 provides structure for the support surface 28, materialreserve 30, feeder 32, material applicator 34, motors 36, and/or theprocessor 38 and may include a base, vertical members, cross members,and mounting points for mounting the above components thereto.Alternatively, the frame 26 may be a walled housing or similarstructure.

The support surface 28 supports the part 100 as it is being constructedand may be a stationary or movable flat tray or bed, a substrate, amandrel, a wheel, scaffolding, or similar support. The support surface28 may be integral with the additive manufacturing system 14 or may beremovable and transferable with the part 100 as the part 100 is beingconstructed.

The material reserve 30 retains additive manufacturing material 40 andmay be a hopper, tank, cartridge, container, spool, or other similarmaterial holder. The material reserve may be integral with the additivemanufacturing system 14 or may be disposable and/or reusable.

The additive manufacturing material 40 may be used for forming part 100and may be in pellet or powder form, filament or spooled form, or anyother suitable form. The additive manufacturing material 40 may be anyplastic, polymer, or organic material suitable for use in additivemanufacturing. For example, the additive manufacturing material 40 maybe acrylonitrile butadiene styrene (ABS), polyamide, straw-basedplastic, or other similar material.

The feeder 32 directs the additive manufacturing material 40 to thematerial applicator 34 and may be a spool feeder, a pump, an auger, orany other suitable feeder. Alternatively, the additive manufacturingmaterial 40 may be gravity fed to the material applicator 34.

The material applicator 34 deposits the additive manufacturing material40 onto the support surface 28 and previously constructed layers. Thematerial applicator 34 may include a nozzle, guide, sprayer, or othersimilar component for channeling the additive manufacturing material 40and a laser, heater, or similar component for melting the additivemanufacturing material and bonding (e.g., sintering) the additivemanufacturing material onto a previously constructed layer. The materialapplicator 34 may be sized according to the size of the pellets, powder,or filament being deposited.

The motors 36 position the material applicator 34 over the supportsurface 28 and previously constructed layers and move the materialapplicator 34 as the additive manufacturing material is deposited ontothe support surface 28 and the previously constructed layers. The motors36 may be oriented orthogonally to each other so that a first one of themotors 36 is configured to move the material applicator 34 in a lateral“x” direction, a second one of the motors 36 is configured to move thematerial applicator 34 in a longitudinal “y” direction, and a third oneof the motors 36 is configured to move the material applicator 34 in analtitudinal “z” direction. Alternatively, the motors 36 may move thesupport surface 28 (and hence the part 100) while the materialapplicator 34 remains stationary.

The processor 38 directs the material applicator 34 via the motors 36and activates the material applicator 34 such that the materialapplicator 34 deposits the additive manufacturing material 40 onto thesupport surface 28 and previously constructed layers according to acomputer aided design of the part. The processor 38 may include acircuit board, memory, display, inputs, and/or other electroniccomponents such as a transceiver or external connection forcommunicating with the processor 16 of the CAD system 12 and otherexternal computers. It will be understood that the processor 38 may beone and the same as processor 16 of the CAD system 12.

The processor 38 may implement aspects of the present invention with oneor more computer programs stored in or on computer-readable mediumresiding on or accessible by the processor. Each computer programpreferably comprises an ordered listing of executable instructions forimplementing logical functions in the processor 38. Each computerprogram can be embodied in any non-transitory computer-readable mediumfor use by or in connection with an instruction execution system,apparatus, or device, such as a computer-based system,processor-containing system, or other system that can fetch theinstructions from the instruction execution system, apparatus, ordevice, and execute the instructions. In the context of thisapplication, a “computer-readable medium” can be any non-transitorymeans that can store the program for use by or in connection with theinstruction execution system, apparatus, or device. Thecomputer-readable medium can be, for example, but not limited to, anelectronic, magnetic, optical, electro-magnetic, infrared, orsemi-conductor system, apparatus, or device. More specific, although notinclusive, examples of the computer-readable medium would include thefollowing: an electrical connection having one or more wires, a portablecomputer diskette, a random access memory (RAM), a read-only memory(ROM), an erasable, programmable, read-only memory (EPROM or Flashmemory), an optical fiber, and a portable compact disk read-only memory(CDROM).

It will be understood that the additive manufacturing system 14 may beany type of additive manufacturing or “3D printing” system such as asintering, laser melting, laser sintering, extruding, fusing,stereolithography, extrusion, light polymerizing, powder bed, wireadditive, or laminated object manufacturing system. The additivemanufacturing system 14 may also be a hybrid system that combinesadditive manufacturing with molding, scaffolding, and/or othersubtractive manufacturing or assembly techniques.

Turning to FIGS. 10 and 11, and with reference to FIGS. 4-9, use of thecomputer modeling and additive manufacturing system 10 for creating acomputer model and united cellular lattice structure 102 of the part 100and forming the part 100 via additive manufacturing according to thecomputer model will now be described in more detail. First, acomputer-aided design of a part volume 200 may be received or generated,in which an overall shape of the part volume 200 may be created, asshown in block 300 of FIG. 10. This may be data representative of awire-frame model, surface model, solid model, or any other suitable CADmodel that defines or exhibits the overall shape of the part volume 200.

The part volume 200 may be divided into a plurality of subvolumes 202,as shown in block 302. The subvolumes 202 each have a number of sides204, each side 204 either adjoining or not adjoining a side of anadjacent subvolume 202. That is, some sides of the subvolumes 202 are“internal” sides (adjoining sides) while some sides of the subvolumes202 are “external sides” (non-adjoining sides) such that the internalsides are positioned within the part volume 200 and the external sidescoincide with portions of a side of the part volume 200. The subvolumes202 may take any suitable shape such as triagonal, quadrilateral,tetrahedral, pyramidal, hexahedral, dodecahedral, or any otherparameterizable polyhedral subvolume shapes.

The subvolumes 202 each have a side combination corresponding to anumber and orientation of subvolumes adjacent thereto. Said another way,the side combinations correspond to a number and orientation ofadjoining sides and non-adjoining sides. For example, a hexahedralsubvolume has sixty-four unique possible side combinations. A subvolumepositioned in a center of the volume would have six adjoining sides andno non-adjoining sides. A subvolume positioned on a corner of the volumewould have three adjoining sides next to each other and threenon-adjoining sides next to each other.

Data representative of a base lattice cell 104 may then be received orgenerated, as shown in block 304. The base lattice cell 104 may be arepeatable structural unit for populating a lattice structure (describedbelow) and may itself be a wire-frame model, surface model, solid model,finite element surface or mesh (e.g., isoparametric or isogeometricfinite elements), face-node connectivity polygonal surface, uniquepolygonal surface, or any other suitable CAD model. The base latticecell 104 may have a shape that at least partially coincides with theshape of the subvolumes. For example, if the subvolumes are hexahedral,the base lattice cell 104 may also be hexahedral. The base lattice cell104 may have a plurality of surfaces. Each surface of the base latticecell 104 may be categorized as either a face surface 106 or an innersurface 108. The face surfaces 106 correspond to faces of the baselattice cell 104 while the inner surfaces 108 do not correspond to facesof the base lattice cell 104. The base lattice cell 104 may have anyshape and may include truss members, cross members, frame-like members,or any other structural components and may have chamfers, fillets,recesses, arches, and complex curves. The base lattice cell 104 may alsoinclude through-holes, channels, voids, chambers, and other negativespaces for allowing fluid to flow therethrough. For example, the baselattice cell 104 may have extruded and non-extruded honeycomb, square,tube, hexahedral, toroidial, or scaffold shapes, or any other suitableshape. The base lattice cell 104 may also include meta-data definingsurface classes and other suitable information.

Data representative of modified lattice cells 110 may then be generatedfrom the base lattice cell 104 for each unique side combination of thesubvolumes, as shown in block 306. That is, face surfaces correspondingto adjoining sides of the side combination are removed and face surfacescorresponding to non-adjoining sides of the side combination are notremoved. It will be understood that the base lattice cell 104 may beformed without face surfaces such that the modified lattice cells 110are generated by adding face surfaces corresponding to non-adjoiningsides of the side combination and not adding face surfaces correspondingto adjoining sides of the side combination. An exemplary calculation ofthe unique side combinations will be described below.

Data representative of modified lattice cell copies 112 (shown insertedinto the subvolumes in FIG. 8) may then be generated according to thenumber of subvolumes having each side combination, as shown in block308. As an example, a cubic volume having twenty-seven subvolumes(similar in appearance to a Rubik's® cube) would require a modifiedlattice cell copy with zero face surfaces (i.e., the central subvolume),six modified lattice cell copies with one face surface (i.e., the sidesubvolumes), twelve modified lattice cell copies with two adjacentsurfaces (i.e., the edge subvolumes), and six modified lattice cellcopies with three adjacent face surfaces (i.e., the corner subvolumes).

The modified lattice cell copies 112 may then be inserted into thecorresponding subvolumes such that the faces of the modified latticecell copies 112 having face surfaces are positioned along non-adjoiningsides of the subvolumes 202, as shown in block 310. The faces of themodified lattice cell copies 112 not having face surfaces are positionedalong adjoining sides of the subvolumes 202.

The modified lattice cell copies 112 may then be merged or joined toform the united cellular lattice structure 102, as shown in block 312.The united cellular lattice structure 102 can then be used to form thepart 100 as described in more detail below.

Portions of the united cellular lattice structure 102 may be modified toconform to the shape of the part or to design changes, as shown in block314. To that end, portions of the united cellular lattice structure 102may undergo smoothing, Jacobian optimization, Laplace optimization,regularity optimization, or other deformations either directly or viamanipulation of the subvolumes 202, as shown in block 302. The unitedcellular lattice structure 102 and/or the subvolumes 202 may also bemanually deformed or edited. Portions of the united cellular latticestructure 102 may be removed or replaced and new sections may be added.Some modified lattice cell copies may need to be replaced with modifiedlattice cell copies corresponding to different subvolume sidecombinations.

The above-described steps may be performed substantially in any orderwithout departing from the scope of the invention. For example, somesteps may be reordered or performed essentially simultaneously.Furthermore, formation of the part volume 200, subvolumes 202, baselattice cell 104, modified lattice cells 110, modified lattice cellcopies 112, united cellular lattice structure 102 may be performed inpre-processing, runtime processing, or post-processing phases. Forexample, the base lattice cell 104 and the modified lattice cells 110may be pre-processed such that only non-duplicate face surfaces areinserted into the subvolumes 202. The base lattice cell 104 and modifiedlattice cells 110 may also be pre-formed and stored a lattice celldatabase such that the base lattice cell 104 and/or modified latticecells 110 are selected for use in the creation of the united cellularlattice structure 102. This may reduce or eliminate the need forrecreating design elements.

The united cellular lattice structure 102 and hence the part 100 maythen be formed via the additive manufacturing system 14, as shown inFIG. 11. First, the additive manufacturing material may be inserted inor positioned on the material reserve 30 of the additive manufacturingsystem 14, as shown in block 400. For example, a spool of the additivemanufacturing material 40 may be loaded onto the additive manufacturingsystem 14.

The additive manufacturing material 40 may then be deposited onto thesupport surface 28 via the material applicator 34 in successive layersaccording to the computer-aided design of the united cellular latticestructure 102, as shown in block 402. To that end, activation ofhorizontally oriented motors in various amounts allows for diagonalmovement and curved movement of the material applicator 34. Activationof a vertically oriented motor may be used for relocating the materialapplicator 34 without depositing material and/or raising the materialapplicator 34 for creation of a new layer (see motors 36, above).

It will be understood that the above-described steps may be performed inany order, including simultaneously. In addition, some of the steps maybe repeated, duplicated, and/or omitted without departing from the scopeof the present invention.

With reference to FIG. 12, an exemplary computation and generation oflattice geometry and part geometry will now be shown. Each step may takeplace during a design phase 500 or a cell insertion phase 502. First,lattice geometry may be received or generated, as shown in block 504. Asurface mesh of the lattice geometry may optionally be created for thelattice geometry, as shown in block 506.

Unique lattice cell face arrangements may then be determined, as shownin block 508. First, n number of periodic faces is determined, as shownin block 510. For example, tetrahedrons have four faces, wedges andpyramids have five faces, and hexahedrons have six faces. These facesform a set S. There are |S|=n elements in the set. A power set P(S) canthen be defined and computed, as shown in block 512. There are|P(S)|=2^(n) subsets of S. As an example, the four faces of atetrahedron can be numbered 1 to 4. These faces form the set S={1, 2, 3,4}. Note that there are |S|=4 elements in the set. The power set of S isP(S)={0, {1}, {2}, {3}, {4}, {1, 2}, {1, 3}, {1, 4}, {2, 3}, {2, 4}, {3,4}, {1, 2, 3}, {1, 2, 4}, {1, 3, 4}, {2, 3, 4}, {1, 2, 3, 4}}. Note alsothat there are |P(S)|=2⁴=16 subsets of S. A power set for a hexahedronwould have |P(S)|=2⁶=64 subsets. Each subset marks the faces to beremoved for one of the unique lattice cell face arrangements, as shownin block 514.

The lattice geometry, surface mesh, and/or unique lattice cell facearrangements may then be used or stored according to a type ofprocessing selected, as shown in block 516. If pre-processing is used,the lattice geometry, surface mesh, and/or unique lattice cell facearrangements may be saved for later use, as shown in block 518. Ifruntime processing or post-processing is used, the lattice geometry,surface mesh, and/or unique lattice cell face arrangements is placed inRAM or otherwise made readily available for use by the processor 16.

Meanwhile, a part geometry and a mesh of the part may be generated orreceived, as shown in blocks 524 and 526. This may be performed alongwith blocks 504 and 506, described above.

Depending on whether pre-processing, runtime processing, orpost-processing is used (block 528), the previously saved lattice cellface arrangements may be loaded into RAM, as shown in blocks 530 and532. For each finite element, face connectivity is then determined, asshown in blocks 534 and 536.

If pre-processing or runtime processing is used, the proper arrangementof face surfaces to insert into the part mesh is determined, as shown inblocks 538 and 540. Importantly, the nodes of the part mesh are uniquenodes. An example of this determination will be described in more detailbelow. Note that the unique lattice cell face arrangements can beaccessed from RAM or other computer memory (block 520 described above).The proper lattice cell faces may then be inserted into the part mesh,as shown in block 542.

If post-processing is used, the base lattice cells may be inserted intothe part mesh, as shown in blocks 538 and 544. The internal facesurfaces may then be removed, as shown in block 546. Determination ofwhich face surfaces are internal will be described in more detail below.Note that the unique lattice cell face arrangements can be accessed fromRAM or other computer memory (block 522 described above).

With reference to FIGS. 13-15, an example of determination of internalface surfaces (i.e., “shared face surfaces”) will now be described inmore detail. This example utilizes eight-node hexahedral finiteelements. Each node is assigned a global node number 1 through 20.

A first finite element (the corner element in FIG. 13) can be evaluatedto determine which of its face surfaces are shared with a face surfaceof another finite element. To achieve this, the nodes of the firstfinite element are analyzed to determine which of them correspond toanother finite element. The nodes of the first finite element may beassigned local node numbers 1 through 8. The faces of the first finiteelement may also be assigned a face number 1 through 8 and a plane X−,X+, Y−, Y+, Z−, and Z+. The faces of the first finite element are alsoassociated with four of the local node numbers. For example, face number1 is associated with local node numbers 3, 8, 7, and 4 and plane X−.

The global node numbers of the first finite element may be compared withthe global node numbers of the other finite elements to determine whichglobal node numbers are associated with other finite elements. In thisexample, global node numbers 1 through 6 and 8 are associated with otherfinite elements. It does not matter with which other finite element theglobal node numbers are associated. It only matters that these globalnode numbers are associated with another finite element. A local nodenumber corresponding to each shared global node number is thenextracted. For the first finite element, local node numbers 1-6 and 8are associated with global node numbers 1-6 and 8. The faces of thefirst finite element in which all of the corresponding local nodenumbers correspond to shared global node numbers are shared faces. Inthis case, faces 2, 4, and 6 (corresponding to planes X+, Y+, and Z+)are shared. For example, face 2 is assigned local node numbers 1, 2, 5,and 6, which all correspond to shared global node numbers. Face 3 isassigned local node numbers 1, 4, 6, and 7. Because local node number 7does not correspond to a shared global node number, face 3 is not ashared face. Note that all of the shared faces of the first finiteelement can be determined together instead of individually. Thissignificantly improves analysis and hence computing efficiency. Theremaining finite elements can then be evaluated in a similar manner todetermine their shared faces.

The above-described face sharing determination can be performed forhigher-order finite elements such as twenty-node hexahedrons. In thiscase, each face must have nine local node numbers that all correspond toshared global node numbers in order to be considered a shared face. Theabove face sharing determination can be performed for 1st order orhigher finite elements and can be used where the finite elements aredeformed or otherwise modified.

The above-described computer modeling and additive manufacturing system10 and method provide several advantages over conventional systems. Forexample, the united cellular lattice structure 102 may be generatedwithout time intensive “search and destroy” removal of shared internalface surfaces. Validity of the cellular lattice structure 102 may easilybe verified via side combination metadata associated with the modifiedlattice cell copies and the corresponding subvolumes. The unitedcellular lattice structure 102 may also easily be modified by replacingmodified lattice cell copies associated with one face combination withmodified lattice cell copies associated with different facecombinations.

Although the invention has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims.

Having thus described various embodiments of the invention, what isclaimed as new and desired to be protected by Letters Patent includesthe following:
 1. A method of generating a computer-based unitedcellular lattice structure comprising the steps of: receiving datarepresentative of a plurality of subvolumes formed from a part volume,each subvolume having a plurality of sides such that the subvolume isconfigured to be positioned adjacent to at least one other subvolume,the plurality of sides including at least one of an adjoining side and anon-adjoining side, the subvolume having a side combinationcorresponding to a number and orientation of adjoining sides andnon-adjoining sides; receiving data representative of a base latticecell having a plurality of surfaces, some of the surfaces being facesurfaces corresponding to faces of the base lattice cell; generatingdata representative of a modified lattice cell from the base latticecell for each side combination of the subvolumes such that each modifiedlattice cell has face surfaces on faces thereof corresponding tonon-adjoining sides and does not have face surfaces on faces thereofcorresponding to adjoining sides; generating data representative ofcopies of the modified lattice cells; and inserting the copies of themodified lattice cells into corresponding subvolumes such that the facesof the modified lattice cell copies having face surfaces are positionedalong non-adjoining sides of the subvolumes and the faces of themodified lattice cell copies not having face surfaces are positionedalong adjoining sides of the subvolumes.
 2. The method of claim 1,wherein the subvolume is hexahedral.
 3. The method of claim 1, whereinthe base lattice cell is generated during a pre-processing phase.
 4. Themethod of claim 1, wherein the base lattice cell is generated during aruntime processing phase.
 5. The method of claim 1, wherein the baselattice cell is generated during a post-processing phase.
 6. The methodof claim 1, wherein the step of generating the data representative ofthe modified lattice cells is performed substantially simultaneouslywith the steps of generating the data representative of the copies ofthe modified lattice cells and inserting the copies of the modifiedlattice cells into the corresponding subvolumes.
 7. The method of claim1, wherein the step of generating the data representative of themodified lattice cells is performed substantially before the steps ofgenerating data representative of the copies of the modified latticecells and inserting the copies of the modified lattice cells into thecorresponding subvolumes.
 8. The method of claim 1, wherein the baselattice cell is a finite element surface.
 9. The method of claim 1,wherein the base lattice cell is a finite element volume mesh.
 10. Themethod of claim 1, wherein the base lattice cell is a face-nodeconnectivity polygonal surface.
 11. The method of claim 1, wherein thebase lattice cell is a unique-polygonal surface.
 12. The method of claim1, wherein the base lattice cell includes meta-data defining surfaceclasses.
 13. The method of claim 1, wherein the step of receiving datarepresentative of a part volume includes creating data representative ofthe part volume via a computer-aided design system.
 14. The method ofclaim 1, wherein the step of receiving data representative of the baselattice cell includes creating data representative of the base latticecell via a computer aided design system.
 15. The method of claim 1,further comprising the step of modifying a shape of at least some of thesubvolumes.
 16. The method of claim 1, further comprising the step ofmodifying a shape of at least some of the copies of the modified latticecells.
 17. The method of claim 1, further comprising the step ofreplacing a copy of a modified lattice cell with a copy of anothermodified lattice cell.
 18. The method of claim 1, further comprising astep of receiving data representative of a part volume, the step ofreceiving data representative of the plurality of subvolumes includingdecomposing the part volume into the plurality of subvolumes.
 19. Amethod of generating a computer-based united cellular lattice structurecomprising the steps of: generating data representative of a partvolume; decomposing the part volume into a plurality of subvolumes, eachsubvolume having a plurality of sides such that the subvolume isconfigured to be positioned adjacent to at least one other subvolume,the plurality of sides including at least one of an adjoining side and anon-adjoining side, the subvolume having a side combinationcorresponding to a number and orientation of adjoining sides andnon-adjoining sides; generating data representative of a base latticecell having a plurality of surfaces, some of the surfaces being facesurfaces corresponding to faces of the base lattice cell, the baselattice cell being created during a pre-processing phase; generatingdata representative of a modified lattice cell from the base latticecell for each side combination of the subvolumes such that each modifiedlattice cell has face surfaces on faces thereof corresponding tonon-adjoining sides and does not have face surfaces on faces thereofcorresponding to adjoining sides, the modified lattice cells beinggenerated during the pre-processing phase; generating datarepresentative of copies of the modified lattice cells, the modifiedlattice cell copies being generated during the pre-processing phase; andinserting the copies of the modified lattice cells into correspondingsubvolumes such that the faces of the modified lattice cell copieshaving face surfaces are positioned along non-adjoining sides of thesubvolumes and the faces of the modified lattice cell copies not havingface surfaces are positioned along adjoining sides of the subvolumes,modified lattice cell copies being inserted into the correspondingsubvolumes during a processing phase.
 20. A system for creating a partbased on a united cellular lattice structure, the system comprising: acomputer modeling system comprising: a processor configured to: receivedata representative of a plurality of subvolumes formed from a partvolume, each subvolume having a plurality of sides such that thesubvolume is configured to be positioned adjacent to at least one othersubvolume, the plurality of sides including at least one of an adjoiningside and a non-adjoining side, the subvolume having a side combinationcorresponding to a number and orientation of adjoining sides andnon-adjoining sides; receive data representative of a base lattice cellhaving a plurality of surfaces, some of the surfaces being face surfacescorresponding to faces of the base lattice cell; generate datarepresentative of a modified lattice cell from the base lattice cell foreach side combination of the subvolumes such that each modified latticecell has face surfaces on faces thereof corresponding to non-adjoiningsides and does not have face surfaces on faces thereof corresponding toadjoining sides; generate data representative of copies of the modifiedlattice cells; and insert the copies of the modified lattice cells intocorresponding subvolumes such that the faces of the modified latticecell copies having face surfaces are positioned along non-adjoiningsides of the subvolumes and the faces of the modified lattice cellcopies not having face surfaces are positioned along adjoining sides ofthe subvolumes; a non-transitory computer readable memory configured tostore the data representative of the base lattice cell, the subvolumes,the modified lattice cells, and the modified lattice cell copiesthereon; a plurality of inputs for receiving inputs from a user; and adisplay configured to visually produce the base lattice cell, thesubvolumes, the modified lattice cells, and the modified lattice cellcopies for allowing the user to inspect and modify the united cellularlattice structure; and an additive manufacturing system configured toform the part via additive manufacturing material deposited layer bylayer according to the united cellular lattice structure.